When prismatic steel frame posts are to be welded at a construction site, it is known to carry out so-called face-to-face welding such that opposite faces of the steel frame post are welded at the same time in order to eliminate possible strains due to welding and provide improved accuracy with respect to construction work. In this case, a rail is placed in a given limited space adjacent to the periphery of the steel frame post so that a welding apparatus is guided by the rail for automatic movement thereon. In this way,.welding is carried out with respect to a joint for the steel frame post.
When welding a joint for a steel frame post in such a manner, mounting a rail to the steel frame post involves laborious work. Especially where the position of the joint is high (e.g., 1m or more) above the surface on which the steel frame post is erected, the welding work involves greater operational inconvenience and more time and labor. When welding work at one side of the steel frame post has been finished, it may be necessary to weld an adjacent side of the steel frame post. In that case, the rail which has been placed at the one side must be removed and placed anew at the adjacent other side, which is very troublesome. Furthermore, welding with respect to any corner portion of the steel frame post must be carried out separately from the welding work at the one and/or the other side. This naturally results in reduced welding efficiency.
Therefore, it is a primary object of the present invention to provide a welding apparatus which eliminates the above mentioned problems.